NETA Power Cable Test Methods 2 — Questions and Answers
Question 1: When performing a DC high-potential test on a shielded cable, where should the voltage be applied?
- Between conductor and shield/ground (Correct answer)
- Between two conductors simultaneously
- To the outer jacket only
- Between the shield and the conduit
Correct answer: Between conductor and shield/ground
DC hi-pot voltage is applied between the conductor and the grounded shield to stress the insulation as it would be in service.
Question 2: Which test method is best suited for locating the position of a fault in an underground cable?
- Time Domain Reflectometry (TDR) (Correct answer)
- Power factor testing
- DC hipot step voltage test
- Insulation resistance megohm test
Correct answer: Time Domain Reflectometry (TDR)
TDR sends a pulse along the cable and measures the reflected signal travel time to pinpoint fault location.
Question 3: A cable's insulation resistance reading drops significantly when corrected to 20°C compared to the reading taken at 40°C. What does this indicate?
- The temperature correction was applied correctly and IR is normal
- The insulation may be deteriorating since temperature correction should increase the reading (Correct answer)
- The cable is acceptable for service
- The megohmmeter is faulty
Correct answer: The insulation may be deteriorating since temperature correction should increase the reading
Insulation resistance decreases with temperature, so a corrected (lower-temperature) value that is still low suggests genuine insulation degradation.
Question 4: What is the primary purpose of a guard terminal on a megohmmeter when testing cables?
- To eliminate surface leakage current from the measurement (Correct answer)
- To boost the output voltage
- To discharge the cable after testing
- To provide a safety ground for the operator
Correct answer: To eliminate surface leakage current from the measurement
The guard terminal diverts surface leakage and connector contamination currents away from the measurement circuit so only bulk insulation current is read.
Question 5: During a VLF (Very Low Frequency) hipot test, what typical frequency is used?
- 0.1 Hz (Correct answer)
- 1 Hz
- 10 Hz
- 60 Hz
Correct answer: 0.1 Hz
VLF testing uses 0.1 Hz to reduce reactive current demand on the test set compared to 60 Hz testing.
Question 6: A cable section shows an absorption ratio (IR1min / IR30sec) of 1.0. How should this result be interpreted?
- Insulation is likely contaminated or wet (Correct answer)
- Insulation is in excellent condition
- The test was performed incorrectly
- The cable has a shorted conductor
Correct answer: Insulation is likely contaminated or wet
An absorption ratio of 1.0 means IR did not increase over time, indicating moisture or contamination is dominating the leakage current.
Question 7: Which NETA standard provides acceptance and maintenance test values for power cables?
- ANSI/NETA MTS
- ANSI/NETA ATS (Correct answer)
- IEEE 400
- NFPA 70B
Correct answer: ANSI/NETA ATS
ANSI/NETA ATS (Acceptance Testing Specifications) provides the tables and pass/fail criteria used during initial commissioning of power cables.
NETA Power Cable Test Methods 2
When performing a DC high-potential test on a shielded cable, where should the voltage be applied?